Where to Place DAs

This section provides suggestions for where to place DAs in different situations.

1. When multicast routing is not enabled and DAs are required to bridge service discovery between subnets

   In this case, a DA must be placed on a host with interfaces and all subnets that share services. The net.slp.interfaces configuration property does not need to be set, unless IP packets are not routed among the interfaces. See Chapter 8, Configuring SLP on Multihomed Hosts for more information on configuring the net.slp.interfaces property.

2. When DAs are deployed for scalability, the primary consideration is optimizing agent access

   UAs typically make many requests for services to DAs. An SA registers with the DA once, and can refresh the advertisement at periodic, but not frequent, intervals. As a result, UA access to DAs is far more frequent than SA access. The number of service advertisements is also usually smaller than the number of requests. Consequently, most DA deployments are more efficient if the deployment is optimized for UA access.

3. Situating DAs so that they are topologically close to UAs on the network to optimize UA access

   Placing UAs topologically close to their DAs reduces the amount of routing delay for answering SLP requests. Naturally, you must configure the DA with a scope shared by both the UA and SA clients.

Placing Multiple DAs for Load Balancing

You can deploy multiple DAs for the same collection of scopes as a means of load balancing. Deployment of multiple DAs is suggested in any of the following circumstances:

• UA requests to a DA are timing out, or are returning with the DA_BUSY_NOW error.

• The DA log shows that many SLP requests are being dropped.

• The network of users sharing services in the scopes spans a number of buildings or physical sites.

You can do a snoop trace of SLP traffic to determine how many UA requests return with the DA_BUSY_NOW error. If the number of UA requests returned is high, which is likely if a single DA is deployed for all users, UAs in buildings physically and topologically distant from the DA can exhibit slow response or excessive timeouts. You might want to deploy a DA in each building to improve response for UA clients within the building.

Links connecting buildings are often slower than the local area networks within the buildings. If your network spans multiple buildings or physical sites, set the net.slp.DAAddresses property in the /etc/inet/slp.conf file to a list of specific host names or addresses so that the UAs access only the DAs you specify.

If a particular DA is using large amounts of host memory for service registrations, reduce the number of SA registrations by reducing the number of scopes the DA supports. You can split a scope having many registrations into two and support one of the new scopes by deploying another DA on another host.